Allow build-time selection between ia32 and x86_64 in the GYP/Xcode Mac Chromium build

Allow build-time selection between ia32 and x86_64 in the GYP/Xcode Mac
Chromium build.

v8.gyp no longer sets any V8_TARGET_ARCH_* macro on the Mac. Instead, the
proper V8_TARGET_ARCH_* macro will be set by src/globals.h in the same way as
the V8_HOST_ARCH_* macro when it detects that no target macro is currently
defined. The Mac build will attempt to compile all ia32 and x86_64 .cc files.
#ifdef guards in each of these target-specific source files prevent their
compilation when the associated target is not selected. For completeness,
these #ifdef guards are also provided for the arm and mips .cc files.

BUG=706
TEST=x86_64 Mac GYP/Xcode-based Chromium build (still depends on other changes)

Committed: http://code.google.com/p/v8/source/detail?r=4666

[Mark Mentovai, 2010-05-14 20:04:01]

Most of this, except for the very last file, is mechanical.

The #ifdef guards all follow the same V8_TARGET_ARCH_* scheme, except the choice
between src/arm/assembler-{arm|thumb2}.cc is handled by checking
V8_ARM_VARIANT_* in addition to V8_TARGET_ARCH_ARM.

[Mads Ager (chromium), 2010-05-17 09:43:13]

Mark, I might be missing something here, but selecting the right files to
compile seems like something the build tools should be able to handle?

There should be no need to have ifdefs like these in every architecture
dependent file so that they can all be included on every build no matter the
architecture.

Shouldn't gyp handle this? Include all the files in the project and do the right
XCode thing to select the files to be compiled for various targets?

[Mads Ager (chromium), 2010-05-17 13:56:07]

LGTM in that case. Thanks for the explanations Mark. I really would prefer not
to have to do this to support XCode. Let me know if you find a way to get rid of
this again. :)